No pics, but here's a list of publications if you can find them:
• Braybrook, AH. An Introduction to the Railway Travelling Post Offices of Japan. Illustrated b/w. Railway Philately, Vol 1 (No 1, pp 14-16, 1966).
• Fujii, K. The Outline of Railway Post Office Postmarks in Japan. Illustrated b/w, 4pp. Publisher?
• Robertshaw, DA. Japanese Railway TPO Cancellations. Illustrated b/w, 12 pp. Published by the author(?), date(?). Based on collections rather than official sources.
• Spaulding, RM Jr. Time Indications in Postmarks. Illustrated b/w, 10 pp. Japanese Philately, Vol 23 (No 4) 1968. Not specifically about TPOs but includes information on how time, direction and trip number were shown in different types of TPO postmarks.
• The Railway Mail Service of Japan. Illustrated b/w. Journal of the TPO & Seapost Society,
Vol 28 (No 3, pp 61-63), Vol 28 (No 5, pp 115-117) 1974. Based on information supplied by Tokyo GPO, 1951.
This might help too - http://railwayphilatelicgroup.co.uk...ry-of-terms/
Scroll down to Japan.